I am biased because I love these two builds but Hydra sorc or Summon Druid are both great fun. The one druid build I've always wanted to Guardian on p8 but have never been able to is the Hunter (summons / bow). I think it could be easy on p1, or average difficulty on p8 for progression only... but full-time p8 I find it incredibly difficult and have died the 3 times I tried it.
Anywho, voted summon druid since I could only choose one.